In a variety of mechanical or structural devices or assemblies including, for example, aircraft, spacecraft and other types of vehicles or vessels; buildings; bridges and other structures, it is frequently desired to be able to determine material properties or changes in material properties of a given part. The design and safe operation of a part depends on having particular properties at particular orientations or locations in the part. Further, any changes in material properties may be indicative of degradation of the part. For example, material stiffness may be an important parameter affecting the performance of a structure. While structures may be designed based on a known initial stiffness of the materials making up the structure, various factors may cause the materials to lose stiffness.
Stress, fatigue and environmental attack such as thermal and/or oxidation processes are just a few of the mechanisms by which a material may be degraded in terms of material stiffness. Fiber/matrix composite materials may be particularly susceptible to stiffness degradation, chiefly through a process known as micro-cracking in which microscopic cracks may develop in the matrix material that binds the fibers together. Such micro-cracking may cause deleterious changes in mechanical properties, stress concentration, and redistribution within the composite material, which in turn may lead to performance degradation, delamination, and fiber damage.
It may be important to quantitatively determine material properties of a plate such as a composite laminate plate along an in-plane direction of the plate, such as to determine its condition at manufacture and/or in-service.
Therefore, it may be desirable to have an apparatus and method that takes into account at least some of the issues discussed above, as well as possibly other issues.